At around 1:20 in my lecture, I mentioned Feynman's interesting comment about boundary layers. He asks why fan blades are always so dusty, despite spinning so fast. Answer: in the boundary layer, the breeze slows down and stops! https://t.co/0ks26IHW9e pic.twitter.com/utlggHbrth
— Steven Strogatz (@stevenstrogatz) March 23, 2021